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![Page 1: 1 Nuclear modification and elliptic flow measurements for mesons at s NN = 200 GeV d+Au and Au+Au collisions by PHENIX Dipali Pal for the PHENIX collaboration.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0221a28abf838cd37fb/html5/thumbnails/1.jpg)
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Nuclear modification and elliptic flow measurements for mesons at sNN = 200 GeV d+Au and Au+Au
collisions by PHENIX
Dipali Palfor the PHENIX collaboration
Vanderbilt University
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Outline
• Motivation
• meson spectra at different centralities
• Nuclear modification factors for the mesons
• Elliptic flow of the mesons
• Summary and outlook
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Baryon/meson puzzle Scaling properties of yields
Different suppression
Elliptic flow Quark number scaling of the elliptic
flow parameter v2
“Mass effect” or “baryon/meson effect”?
Au + Au @ √sNN = 200 GeV
PHENIX
Motivation: Baryon/meson anomaly
meson has a mass similar to a proton.
Appropriate probe to address the baryon/meson puzzle.
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K+K- measurement in PHENIX
Number of events analyzed:
Spectra: 409 M for TOF
170M for PbSc
Elliptic flow: 800 M
separation in TOF0.3 < p (GeV/c) < 2.5
separation in EMCal: 0.3 < p(GeV/c) < 1.0
Four independent K+K- pairing
TOF – TOF (9% of the total ’s)TOF – PbSc (East) (27% of the total ’s)PbSc(East) – PbSc(East) (9% of the total ’s)PbSc(West) – PbSc(West) (55% of the total’s)
Allows a self-consistent measurement on .
K+K- pairing topology
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meson reconstruction technique
Combinatorial background (CB) is estimated by event mixing.
Normalized to 2(N++.N--), N++ and N– are like sign measured yields.
Signal = Same event - CB
Experimental mass resolution ~ 1 MeV/c2
Better than mass width.
Subtracted spectrum is fitted with Relativistic Breit Wigner convolved with Gaussian mass resolution.
Centroid and width are consistent with PDG.
Number of mesons analyzed Spectra: ~ 44KElliptic flow :~ 180K
<m> = 1.01891 ± 0.00003 (stat) ± 0.00085 (syst) GeV/c2
= 4.22 ± 0.09 (stat) ± 0.506 (syst) MeV/c2
Subtracted spectrum
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• Raw yield extraction N (rec) (mT) = Same event (mT) – CB(mT) Yield is extracted by integrating the subtracted mass
spectrum over a fixed mass window of ± 5 MeV with respect to the centroid.
Optimized signal and S/B ratio.
• Corrections– Acceptance: K+K- pair MC through PHENIX simulation chain.– Efficiency: time (experimental run) dependent variations.– Occupancy dependent corrections: Embedding simulated
K+K- pairs into the real data.
Spectra: raw yields to absolutely normalized spectra
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Minimum-bias spectra
• Excellent agreement between the subsystems
• Understanding of the systematics.
• Run4 result is consistent with Run2.
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meson spectra at different centralities
Talk by A. Kozlov [6(b)]
Poster by D. Pal (158)
Centrality dN/dy T (MeV)
MB 1.08 ± 0.04 ± 0.20 388 ± 5 ± 27
0-10% 3.80 ± 0.30 ± 0.72 372 ± 11 ± 26
10-20% 2.32 ± 0.16 ± 0.44 394 ± 10 ± 27
20 – 30% 1.62 ± 0.11 ± 0.31 397 ± 10 ± 28
30 – 40% 0.95 ± 0.07 ± 0.18 401 ± 10 ± 28
40 – 50% 0.75 ± 0.04 ± 0.13 377 ± 8 ± 26
50 – 60% 0.35 ± 0.03 ± 0.06 392 ± 12 ± 27
60 – 90% 0.11 ± 0.01 ± 0.02 348 ± 11 ± 24
0.0074 ± 0.0007 ± 0.0020 391 ± 25 ± 50pp
Au
+ A
u @
200
GeV
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Scaling of protons and spectra
Ncoll scaled spectra vs pT compared to protons
Radial Flow at low-pT At intermediate pT, (anti)protons scale with Ncoll
No Ncoll scaling for Baryon/meson effect? Or mass effect?
Quantify nuclear effects by Central-to-peripheral ratios (Rcp) andratio of Au-Au central to pp yields (RAA).
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Two extreme centrality classes show Completely different scales of suppression.
Mesons ( and ) in Au+Au 0 – 10% (most central) are suppressed to the same extent.
They are least (or almost not) suppressedin 60-90% (most peripheral)
Protons are not suppressed anywhere.
Baryons and mesons show a clear difference.
pp
AuAuAA Yield
)Ncoll/Yield(R
What about other centralities?
Suppression of the mesons decreasesfrom central to peripheral.
Two extreme centrality classes show completely different scales of suppression.
Mesons ( and ) in Au+Au 0 – 10% (most central) are suppressed to the same extent.
They are least (or almost not) suppressed in 60-90% (most peripheral)
Suppression of mesons increases from peripheral to central.
Protons are not suppressed anywhere.
Baryons and mesons show a clear difference.
Nuclear modification factors, RAA
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Nuclear modification factor, Rcp
Peripheral
Centralcp )Ncoll/Yield(
)Ncoll/Yield(R
Au + Au collisions show suppressionsfor mesons( and ) and no suppression for the protons and ’s.
d+Au collisions (cold nuclear matter) shows no suppression for baryons or mesons.
The anomalous meson suppression is a property of the hot and dense matter.
d + Au @ √sNN = 200 GeV
Au + Au @ √sNN = 200 GeV
Poster by D. Pal (158), D. Mukhopadhyay (154)
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Elliptic Flow of baryons and mesons
At low pT hydro works remarkably well
Above ~ 2 GeV/c : a split between mesons and baryons
Universal behavior in flow per quark: expected from recombination
Need to measure v2 of
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• Event reaction plane is determined by beam beam counter -- BBC South and BBC north
Peripheral Central
100 – centrality(%)100 – centrality(%)
Peripheral Central
• Reaction plane resolution:sqrtcos2BBCSBBCN
Reaction plane
Extraction of uncorrectedv2 from azimuthal distribution
Reaction plane resolutioncorrection factor
v2 = v2(obs).
v2 measurement in PHENIX
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v2 extraction of
Azimuthal distribution of mesonsFitted with the function:
dN/d()=A [1+2v2(obs)cos2()]
The p1 parameter in the figure is the uncorrected v2.
v2(obs)v2 = R.P. Resolution correction
1.0 < pT (GeV/c) < 1.5 1.5 ≤pT (GeV/c) < 2.0 2.0 ≤pT (GeV/c) < 3.0
v2(obs) = 0.0250 +/- 0.0137v(obs) = 0.0338 +/- 0.0091v2(obs) = 0.0198 +/- 0.0071
Minimum bias Minimum bias Minimum bias
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v2 vs pT
Non-zero v2 observed for mesons
Statistically, it is consistent withother hadrons.
Minimum bias
With present error bar, the quarknumber-scaled meson v2 is
consistent with other hadrons.
Talk by H. Masui, Poster by A. Taranenko (identified hadron v2)
PHENIX Preliminary
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Summary• PHENIX has measured mesons in K+K- decay channel with its full
central arm. K+K- spectra at seven centrality bins have been measured within
1.2 < mT (GeV/c2) < 4.4.
• Nuclear modification factors, Rcp and RAA
in Au-Au collisions exhibits dramatic suppression of ’s like other mesons.
• Rcp in d-Au clearly demonstrate absence of any suppression for the mesons.
• v2 ofhas been measured for the first time. It is non-zero for intermediate pT.
v2 of scaled with number of quark follows universal quark number scaling within statistical errors.
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Outlook
Considerable improvements expected over the next few months
- A factor of 4 increase in statistics for spectra analysis:finer pT bins and a wider range
- Measurement of v2 as a function of centrality
- Fine tuning of the cuts and additional statistics for elliptic flow analysis may enable us to increase statistical significance of the v2 signal.
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Backup slides
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v2 analysis methods• Method 1: dN/d( = A(1+2v2(obs)cos2( – 2)) -- Fit azimuthal distribution of with this function with v2 as a fitting parameter.
• Method 2: v2 (obs) = <cos2(2)> for the mesons. Methods 1 and 2 are mathematically equivalent.
• Method 3: Mesure v2 from the azimuthal distributions of the same event and CB and then extract
uncorrected v2 ofas: v2(obs) = [NS+B v2(S+B) – NB v2(B)]/NS
S+B = Signal + CB
v2 = v2(obs)/ = Reaction plane resolution = 1/sqrt(2 <cos2(2(BBCS) – 2(BBCN))>)
Three methods have extracted the same v2 value for Phi mesons.Method 1 has been applied to the full statistics of the data.
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KK in pp collisions: Comparison with STAR